14 BIOTIC STRUCTURE AND BIOTIC ENERGY 



spending increased pressure of the chemical substances formed, 

 and finally a point is reached at which, without external aid, the 

 discharge commences spontaneously. 



A most interesting and beautiful example of such a rhythm 

 dependent upon external stimulation under normal conditions, 

 but capable of heaping up and becoming automatic in the absence 

 of the usual stimulus or its delayed appearance beyond the accus- 

 tomed time, is found in the case of the phosphorescent organisms 

 so abundant in our seas, especially in the autumn months. 



It might be supposed at first thought that these organisms are 

 not observed to emit light during the day because of the presence 

 of daylight, and that if taken into a dark room they would be found 

 to be phosphorescent just as brilliantly as at night. This is, how- 

 ever, not the case ; not a spark can be elicited from them even by 

 vigorous agitation so long as there is daylight in the outer world. 

 But if one stands by, and watches in the dark room as twilight is 

 falling outside, although the organisms have not been exposed to 

 light all day, one observes the little lamps light up and flash out one 

 by one like coruscating diamonds in the darkness, till the whole 

 dish becomes studded with flashing and disappearing lights, a 

 glorious sight in the darkness and stillness. Nor is any agitation of 

 the water required to call forth sparkling, although the already 

 rhythmically lighting up organisms are, as is well known, stimulated 

 to greatly increased activity by such mechanical disturbance. Still, 

 without any disturbance whatever the organisms continue at 

 regular intervals to emit bright flashes which slowly fade away and 

 disappear until a new flash at the same spot once more appears, 

 somewhat resembling a revolving light seen some distance off at 

 sea. The appearances are such as would follow the expression from 

 a minute gland duct of small drops of a phosphorescent secretion 

 at regular intervals. 



At daybreak the series of changes are the reverse of those 

 witnessed at dusk ; if the dish containing the phosphorescent organ- 

 isms be observed from about an hour before sunrise, it will be seen 

 that at first the organisms are still flashing out brilliantly, but about 

 half an hour before sunrise the number of flashes begins rapidly 

 to diminish, and at sunrise there are hardly any showing. For 

 another half-hour or so flashes can still be evoked by violent 

 mechanical agitation of the water, but later no amount of agitation 

 will call forth a single flash. 



